1. Field of the Invention
This invention relates to a smelting process of recovering metal from non-ferrous metal oxide ores or concentrates and/or from fine-grained non-ferrous metal sulfide ores or concentrates, particularly from non-ferrous heavy metal sulfide ores or concentrates, wherein sulfide ores are oxidized with a supply of air and/or oxygen, and to apparatus for carrying out that process.
2. Description of the Prior Art
Such non-ferrous metal oxide ores may become available in granular or lump form but are produced, as a rule, from sulfide ores by an oxidizing roasting process. The roasting results in a production of sulfur dioxide in large quantities, which must be separately processed, e.g., to produce sulfuric acid. The pyrometallurgical processing of oxide starting materials in the form of lumps has previously been effected, as a rule, in low shaft furnaces used to produce blister copper or black copper. The gas formed in a low shaft furnace under reducing conditions consists, as a rule, of nitrogen, carbon dioxide and various sulfur compounds, such as SO.sub.2, H.sub.2 S, COS and CS.sub.2. The CO content of such exhaust gases is relatively low in most cases so that the exhaust gas has only a low calorific value. Non-ferrous heavy metal oxide ores can be reduced much more easily, as a rule, than iron oxide ores.
U.S. Pat. No. 3,948,639 describes a process and apparatus for smelting sulfide ores or concentrates in such a manner that the gases leaving the smelting furnace and the sulfide ore or concentrate are jointly supplied to a pretreating zone, from which the cooled gases are supplied to the upper end of the reaction zone of the smelting furnace for a recovery of sulfur and of the pretreated sulfide ore or concentrate.
French Patent Specification No. 2,128,053 describes a process and apparatus for recovering metals, particularly nickel, from ores, in which the metal is segregated in a fluidized bed by a combustion with air and a low-hydrogen fuel, such as coke.
For a reduction of iron ores with the aid of inexpensive fuels it has already been proposed to feed prereduced iron ore in the form of sponge iron directly to a melting gasifier, in which a fluidized bed of relatively low-grade coal is maintained and is used to decompose residual oxides and to generate the heat required for smelting.
In copper metallurgy, a number of processes have been proposed in which sulfide concentrates are directly oxidized in a melting burner with a generation of energy at a high rate. That solids-firing burner served for a simultaneous roasting and smelting of the concentrates to form matte. In succeeding settling hearths, the matte was separated from the slag. A disadvantage of that process resides in that SO.sub.2 becomes available as a gaseous combustion product and must be utilized, e.g., in a plant for producing sulfuric acid. Besides, metal is lost at a high rate in the slag because a large proportion of the metal is dissolved as Cu.sub.2 O in the slag under the oxidizing conditions prevailing in the smelting vessel. Other processes of treating non-ferrous metal ores require oxide ores as starting materials and the low shaft furnace operating under reducing conditions is the smelting equipment most widely used for that purpose.
It has also been proposed to operate reducing process stages in succession to suspension melting processes although such arrangement involve complicated flow paths for the exhaust gases because the oxidizing exhaust gases from the cyclone and the reducing exhaust gases from succeeding melting chambers or furnaces must be conducted in separate lines.